The term "clay" as used in various areas of technology, is subject to wide variations in meaning. However, an inclusive definition normally would be a naturally occurring sedimentary material generally composed of hydrated silicates of aluminum, iron or magnesium and often containing hydrated alumina and iron impurities. The particles of a clay are typically of at least near-colloidal size in at least one dimension (platelets are typical) and commonly develop thixotropic flow properties when sufficiently pulverized and wetted.
The organization of clay types remained somewhat poor until the development of satisfactory x-ray techniques for studying the atomic structure of individual clays. A paper: Kaolin Materials, U.S. Geological Survey Professional Paper 165-E, C. S. Ross and P. F. Kerr, 1930, pp. 151 to 176, is widely recognized as the beginning of a systematic approach to clay mineralogy. The monograph "Crystal Structures of Clay Minerals and their x-ray Identification" edited by G W. Brindley and G. Brown for the Mineralogical Society, is the most convenient standard reference. More recent work has been reviewed in a Mineralogical Society of American Monograph (Reviews in Mineralogy, Vol. 16, "Hydrous Phyllosilicates, Ed. S. W. Bailey, (1988)).
Included in the classes of clay minerals are smectite clays and kandite clays, the latter synonymously called diazeolites, serpentines, septochlorites and a variety of other specific names, depending on composition and layer orientation.
Smectites generally layered clays represented by the general formula: EQU (Si.sub.8).sup.iv (Al.sub.4).sup.vi.sub.O20 (OH.sub.4)
where the IV designation indicates an ion coordinated to four other ions, and VI designates an ion coordinated to six other ions. The IV coordinated ion is commonly Si.sup.4+, Al.sup.3+, or Fe.sup.3+ but could also include several other four coordinated ions, e.g., P.sup.5+, B.sup.3+, Ge.sup.4+, Be.sup.2+, etc. The VI coordinated ion is typically Al.sup.3+ or Mg.sup.2+, but could also include many other possible hexacoordinate ions, e.g., Fe.sup.3+, Fe.sup.2+, Ni.sup.2+, Cl.sup.2+, Li.sup.+, etc. The charge deficiencies created by substitutions into these cation positions are balanced by one or more cations located between the structured platelets. Water may be occluded between the layers and either bonded to the structure itself or to the cations as a hydration shell. Commercially available clays typical of this class include natural and synthetic variants of montmorillonite, bentonite, hectorite and various mica or mixed mica-montmorillonite mixed phases, including synthetic varieties, the most common being materials such as SMM (synthetic mica-montmorillonite) originated by the Baroid Corp. The pillaring of said materials is well established and characterized (e.g., U.S. Pat. Nos. 4,176,090; 4,248,739; and 4,271,043) and the state of the art has recently been reviewed by Vaughan (Amer. Chem. Soc. Symp. Ser. #368, p. 308-323, (1988)), particularly as the basic concept has been applied to layer compounds other than clays.
Kandite clays, also often called "kaolinite" minerals, are made up of 1:1 layers of tetrahedrally oxygen coordinated silicon, bonded to layers of octahedrally bound cations. In kaolinite, dickite and nacrite all of the tetrahedral cations are Si.sup.4+ and all of the octahedral cations are Al.sup.3+ ( so called dioctahedral forms ). However, in the serpentinite varieties, major substitution of Al.sup.3+ and Fe.sup.3+ occurs for Si.sup.4+ in the tetrahedral layer and a range of di- and trivalent cations substitutes for Al.sup.3+ in the octahedral layer. The ion Mg.sup.2+ is typically substituted for Al.sup.3+, although any of the Fourth Period Transition elements, e.g., V, Cr, Mn, Fe, Co, Ni, Cu, Zn, may serve as substitutes. In some locations they may form major deposits, as in the case of garnierite, a major nickel ore. (Table 1 lists examples of various mineral kandites illustrating the multiplicity of chemical compositions. ) A main characteristic of the class is that each member generally has a 1:1 neutral layer. The ideal stoichiometry of the dioctahedral (kaolinite) and trioctahedral (chrysotile) end-members may be given respectively as: EQU Al.sub.2 Si.sub.2 O.sub.5 (OH).sub.4 EQU and EQU Mg.sub.3 Si.sub.2 O.sub.5 (OH).sub.4
TABLE 1 ______________________________________ EXAMPLES OF KANDITE MINERALS KAOLINS-SERPENTINES VI IV ______________________________________ Kaolin Al.sub.2 Si.sub.2 O.sub.5 (OH).sub.4 Halloysite Al.sub.2 Si.sub.2 O.sub.5 (OH).sub.4 Chrysotile Mg.sub.3 Si.sub.2 O.sub.5 (OH).sub.4 Garnierite Ni.sub.3 Si.sub.2 O.sub.5 (OH).sub.4 Amesite (Mg, Fe).sub.2 Al Si Al O.sub.5 (OH).sub.4 Cronstedtite (R.sub.3-x.sup.2+, Fe.sub.x.sup.2+) Si, Fe.sup.3+ O.sub.5 (OH).sub.4 Greenalite (Fe, Mg, Mn).sub.3 Si.sub.2 O.sub.5 (OH).sub.4 ______________________________________
Mixed layers are common, as they are in all clay mineral types. However, Kaolin is quite unique as a mineral in that it exists in very high purity deposits in many parts of the world. The deposits in the states of Georgia and North and South Carolinas are particularly famous; the single layer thickness of this repeating sheet is about 7.2 .ANG.. When layers of water separate the 1:1 sheets, the repeat sheet dimension expands to about 10.1 .ANG., as is seen in the halloysite variety of kaolinite. Halloysite in comparison is a relatively rare mineral in large deposits and rapidly irreversibly loses water on exposure to air. PG,7
Sorption of various organic molecules, such as glycerol, have been reported for kaolinite and the 2:1 smectite clays. Organic molecules do not as a rule produce permanent pillaring between the clay layers, but form intercalates which may exhibit molecular sieve properties in some cases, as described by R. M. Barrer (Clays and Clay Minerals, v. 37, p. 385-95 (1989)) and Theng ("Formation and Properties of Clay Polymer Complexes, Elsevier Press" (1979)), but readily lose such properties on heating to moderate temperatures. Similarly, intercalation of organic salts, e.g., potassium acetate, has been reported and are reviewed by MacEwan and Wilson (ibid, p. 236) and Barrer (Zeolites and Clay Minerals p. 407, 1978). Permanent pillaring has not been reported in 1:1 kandite materials hitherto, and is the principal focus of this invention.
Various non-kandite clays have been expanded to produce pillared materials. For instance, smectite-type clays treated with large cationic inorganic complexes result in large pore materials useful as sorbents and catalysts. See Vaughan et al, U.S. Pat. No. 4,176,090, issued Nov. 27, 1979 (hereinafter Vaughan '090); Vaughan et al, U.S. Pat. No. 4,248,739, issued February 3, 1981 (hereinafter Vaughan '739); and Vaughan et al, U.S. Pat. No. 4,271,043, issued Jun. 2, 1981 (hereinafter Vaughan '043).
Vaughan '090 is directed to the production of stable interlayered clay compositions which are prepared by reacting smectite-type clays with polymeric cationic hydroxy metal complexes of metals such as aluminum, zirconium, or titanium and mixtures of those. The resulting pillared smectites have pillars of about 6 to 16 .ANG. between the clay layers. The resulting internal interconnected micropore structure (within the layer) has a majority of pores which are less than 30 .ANG. in diameter. Vaughan '090 makes no mention of using kandite-type clays as starting material.
Vaughan '739 discloses a method for producing pillared interlayered smectite clays which is an improvement upon the method for producing pillared materials disclosed in Vaughan '090. The improvement is said to lie in the use of an interlayering compound which is a polymeric cationic hydroxy inorganic metal complex having an increased molecular weight in excess of about 2,000 to about 20,000. The resulting clay products have interlayer spacing of about 6 to 16 .ANG. and have 80% of their pores less than about 40 .ANG. in diameter. Again, Vaughan, '734 makes no suggestion of using kandite-type clays as starting material.
Vaughan '043 teaches a variation on the processes and products of Vaughan '090 and Vaughan '739 which entails treating the calcined products disclosed in those latter patents with a basic solution of a compound such as ammonia. The products treated in this manner are disclosed to have an enhanced ion exchange capacity. Vaughan '043 makes no suggestion of using a kandite-type clay as starting materials. A complete review of these patents has been published elsewhere (Catalysis Today, V. 2, p. 187-98, (1988)).
The disclosure in U.S. Pat. No. 4,060,480, to Reed et al, issued Nov. 29, 1977, suggests treating generally smectite-type materials with a aluminum compound, drying the product and calcining it to produce a clay having an expanded interlayer separation. Reed et al suggest that a gibbsite-like layer may be formed by such a treatment. No mention is made, however, of treating a kandite material in such a fashion.
Various modified hydrotalcite like materials (sheet structures related to clays) have also been subject to "pillaring" in various ways (U.S. Pat. No. 4,454,244). These materials are single sheet octahedral structures having a positive layer charge, and are therefore subject to pillaring reactions with anionic species ( e.g., U.S. Pat. No. 4,454,244).
Recently several new layer structures have been successfully pillared with a variety of anionic, cationic and neutral inorganic polymeric molecules. They include various clays such as rectorite (European Patent Appln. 197,012) and tetrasilicia mica (Japanese Patent 56-142982); sheet silicic acids (European Patent Appln. 222,597; Deng et al, Chemistry of Materials, v. 1, p. 640-50, (1989)) which comprise a very large group of material (see F. Liebau for a review of such materials in "Structural Chemistry of Silicates" (Springer-Verlag (1985)); and zirconium phosphates (European Patent Appln. 159,756).
Several recent reviews of pillaring in clays and related sheet structures (Pinnavia, Science, 220, p. 365, (1983); Vaughan, "Catalysis Today", vol. 2, page 187-198, 1988; Vaughan, in "Perspectives in Molecular Sieve Science" Ed W H Flank et al, ACS Symp. Ser. 368, p. 308-23 (1988)) do not report kandite pillaring. Based on the viewpoint that pillaring requires a charge deficiency on the layer, the kandites would not be expected to be suitable pillaring substrates, as they are not recognized as having layer charge, and therefore have no ion exchange capacity. Reactivity and exchange in these materials is generally related to `OH` groups at the edges of the crystals. I have discovered that these can indeed be pillared to form porous materials. The proposed structure is shown in FIG. 1, which compares a kandite with a hydrated kandite and a pillared interlayered kandite (PILK).